1. Field of the Invention
One aspect of the disclosed invention relates to memory devices and a manufacturing method thereof.
2. Description of the Related Art
A technique by which transistors are formed using semiconductor thin films formed over a substrate having an insulating surface has attracted attention. Transistors are used for display devices (typically, a liquid crystal television), memory devices where memory elements are arranged in matrix, and the like. Silicon is known as a material for a semiconductor thin film applicable to a transistor; however, an oxide semiconductor has attracted attention in recent years (see Patent Document 1).